1. Field of the Invention
The invention pertains generally to imaging using multiple bands of radiation and particularly to the simultaneous imaging of multiple bands of radiation to form a scene for viewing by a user.
2. Description of Related Art
Currently, an individual seeking to view objects in dark, low level light conditions and/or poor atmospheric conditions, may rely on either image intensification sensors for the visible/near-wavelength infrared (“referred to hereafter as VIS/NIR”) or thermal infrared (IR) sensors. Further, within the IR range, separate detectors are necessary in order to detect both mid-wavelength IR (“MWIR”) and long-wavelength IR (“LWIR”). No single detection system allows an individual to simultaneously view any two of these wavelength ranges. Each sensor, independently, has significant advantages in, for example, a wide variety of military scenarios. The IR is better at detecting all types of items (e.g., targets) under most light level and meteorological conditions. Camouflage and obscurants are much less effective in the thermal band than in the VIS/NIR. However, many night missions, especially those in urban settings, favor the image intensification due to the need to read signs (e.g., alphanumerics), see through glass windows, and recognize and differentiate individuals. Unlike VIS/NIR sensors, thermal imagers do not detect lasers operating at 1.06 microns. This is significant because such lasers are used for target ranging and designation. Knowledge of such illumination by friendly or enemy forces can be vital. In addition, image intensification sensors operating in the VIS/NIR (i.e., 0.6 to 1.1 micron range) offer considerably better resolution than the IR sensors.
Uncooled IR sensors (both currently existing and those improvements in development) offer a low cost, low power approach to thermal imaging. Operating in the long wave infrared (LWIR: 7.5 to 14 microns), uncooled thermal imaging is excellent for many military applications because items of interest (e.g., enemy soldiers, vehicles, disrupted earth) almost always emit more in-band (in this case IR) energy than the background. Other applications for uncooled thermal imaging include security, hunting, monitoring and surveillance, firefighting, search and rescue, drug enforcement, border patrol and ship navigation. The current uncooled devices and even those in development (e.g., 640×480 with 25 micron pixels) have significantly lower resolution compared to image intensification (II) devices or daytime telescopes.
Image intensifiers take whatever amount of light is available (e.g., moonlight, starlight, artificial lights such as street lights) and electronically intensify the light and then display the image either directly or through the use of an electronic imaging screen via a magnifier or television-type monitor. Improvements in II technology have resulted in the GEN III OMNI IV 18-mm tube offering the equivalent of more than 2300×2300 pixels. II covers the visible and near infrared (VIS/NIR: 0.6 to 1.1 microns) and overcomes the LWIR limitations listed above. However, II is limited by the ambient light available, targets are harder to find, and camouflage/obscurants (e.g., smoke, dust, fog) are much more effective. While scientists have long seen the complementary nature of LWIR and II to achieve sensor fusion, most attempts involve the use of two parallel sensors and sophisticated computer algorithms to merge the images on a common display, a display with lower resolution than the II tube. This approach is difficult to implement for an individual handheld sensor. Currently, for example, night operations forces often carry both II and LWIR sensors, each with different fields of view and magnification, for special reconnaissance, target interdiction, and strike operations. The synergy noted above is lost because the soldier cannot use the devices simultaneously.
IR imaging devices typically provide monochrome imaging capabilities. In most situations, the ideal viewing scenario would be full color. This is of course achieved in the visible band. There are numerous situations where a user alternates between visible band viewing scenarios and IR band viewing scenarios within the span of seconds. Current imaging devices do not allow a user to either: (a) simultaneously view both the monochrome IR image and the full color visible image, or (b) change between IR monochrome imaging and full-color visible imaging without mechanically altering the imaging device or removing the device from the users field of view (e.g., as in the case of an IR helmet mounted sensor).